The present invention relate to a microwave filter composed of at least two cavity resonators in which energy is propagated in at least one TE or TM mode, with a coupling aperture provided between two adjacent cavity resonators coupling together the two modes of the two cavity resonators.
Such a microwave filter is disclosed, for example, in U.S. Pat. No. 3,697,898 and in IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol. MIT-32, No. 11, November, 1984, pages 1449-1354. The resonant circuits of the microwave filters forming the basis of these disclosures are realized by TE and/or TM modes which oscillate in resonance in the individual cavity resonators. The characteristic of such a microwave filter depends on which mutually orthogonally polarized modes exist in the individual cavity resonators and which of these modes are coupled together. There are couplings between the modes existing in an individual cavity resonator and couplings between modes in different cavity resonators. Mode couplings taking place from cavity resonator to cavity resonator are effected by way of coupling apertures equipped with coupling irises.